Welcome to the forum!
You might find an owner's manual if you look near the bottom of the page under the red banner that says "Library", and under that in the sub-forums, there's a button for "Hi Lo Owner's Manuals". Check for something in the range of 1983. Hi-Lo's didn't change drastically from year to year, so chances are that you'll find something in that era that will be very useful.
There is also a collection of videos that are very informative, around 30 individual videos in total. They can be found here:
As to the buttons near the back window, I bet someone here will have a trailer of about that age to answer your question. Sometimes, posting a photo helps, but I bet someone will be able to answer it shortly.